1. Field of the Invention
The invention relates to the preparation of citric acid and of salts of citric acid.
2. Description of the Prior Art
Citric acid or its salts are useful in different ways as exemplified by the following patents: as a plasticizer, U.S. Pat. No. 2,409,703; as a bleaching agent, U.S. Pat. No. 2,529,831; as a food antioxidant, U.S. Pat. No. 2,563,855; as a detergent component, U.S. Pat. No. 2,765,280.
The principal prior sources of citric acid and its derivatives are recovery from natural products such as citrus fruits and production via micological or fermentation processes. The recovery of citric acid from natural products or sources is disclosed in U.S. Pat. Nos. 2,027,264; 2,193,904; and 2,396,115. The production of citric acid by micological processes is disclosed in U.S. Pat. Nos. 2,353,771; 2,739,923; 2,883,329 and 3,335,067.
Heretofore the chemical synthesis of citric acid or of its salts has proved to be very difficult. In fact, the only known U.S. Pat. relating to a chemical synthesis of citric acid is No. 3,356,721 which issued in 1967 and there is nothing in the patent to show that a significant yield of citric acid or its salts is obtained with the process described therein. Since the amount of natural source citric acid is limited, there has been a need in the art for a commercially attractive chemical synthesis process for producing citric acid or its salts.